After Nashville (Tennessee) Metro Water Services completed a sewer rehabilitation project in 1996, a long-term study showed that rehabilitation effectiveness decreased 7% over 12 years.

Early results showed 620 million gallons of infiltration, or approximately 35% of inflow and infiltration, were removed annually. At the end of the study, that number was down to about 28%, or 488 million gallons.

“The results could suggest that the level of effectiveness has...